Request for reduction of manufacturing cost, higher performance and reduction of size and weight of the electrical rotating machines for general industrial use such as dynamos has become increasingly strong. In order to satisfy these requirements, quests have been made for various approaches such as optimization and simplification of coil designing and insulating composition, and optimization of the insulation system for the rotating machine stators (mostly composed of insulation coil and iron core). Typically, single prepreg system, single impregnation system and vacuum pressure impregnation system, as briefly described below, are adopted for the insulation of stators.
(1) In the single prepreg system, a prepreg mica tape is wound around an insulation coated conductor shaped into a regulated configuration, and heat cured to form an insulation coil, and this insulation coil is housed in an iron core slot and fixed in position by a pile or a pile liner to thereby constitute a stator.(2) In the single impregnation system, an insulating mica tape is wound around an insulation coated conductor shaped into a regulated configuration to form a single insulation coil, and it is impregnated with an epoxy resin composition in vacuo under pressure, followed by heat curing to make an insulation coil. This insulation coil is housed in an iron core slot and fixed by a pile or a pile liner to constitute a stator.(3) In the vacuum pressure impregnation system, an electrically insulating mica tape is wound around an insulation coated conductor shaped into a regulated configuration to make a single insulation coil, and it is incorporated in an iron core slot, fixed therein by a pile or a pile liner and connected at the outer end of the iron core for integration. An epoxy resin composition is vacuum pressure impregnated in the integrated single insulation coil and iron core, and then the epoxy resin composition is heat cured to constitute a stator.
The electrically insulating mica tape used for the said single impregnation system or vacuum pressure impregnation system is generally composed of mica, a reinforcing layer such as glass cloth or organic material film, a binder resin for bonding these mica and reinforcing layer, and a curing catalyst for the epoxy resin composition impregnated in the mica tape.
JP-A-11-215753 (Patent Document 1) discloses an insulating mica tape used for the insulation coils which is featured by a prolonged shelf life realized by using a phenol resin in lieu of an epoxy resin as a binder resin and a shortened gel time achieved by using an imidazole compound or zinc naphthenate as a curing catalyst for the impregnating epoxy resin composition.
In the prepreg sheet for the metallized laminates or wiring boards disclosed in JP-A-2004-307761 (Patent Document 2), a biphenyl type epoxy resin is used as the impregnating resin and an imidazole compound or zinc naphthenate is used as a curing catalyst to realize enhancement of glass transition temperature (Tg) as well as improvements of peel strength and dielectric properties.
In the insulating mica tape for electric devices disclosed in JP-A-11-213757 (Patent Document 3), an elongation of shelf life is realized by applying a curing catalyst on the base glass fiber and coating the periphery of the curing catalyst with a thermoplastic resin which does not cause a curing reaction with the catalyst while using an imidazole compound or zinc naphthenate as said curing catalyst.    Patent Document 1: JP-A-11-215753    Patent Document 2: JP-A-2004-307761    Patent Document 3: JP-A-11-213757